var Board = React.createClass({

  render: function() {

    var className = "board";

    if (this.props.selected) {

      className += " selected";

    }

    return (

      <div className={className}>

        {this.props.index + 1}

      </div>

    );

  }

});

​

var BoardSwitcher = React.createClass({

  render: function() {

    var boards = [];

    for (var ii = 0; ii < this.props.numBoards; ii++) {

      var isSelected = ii === 0;

      boards.push(

        <Board index={ii} selected={isSelected} key={ii} />

      );

    }

    return (

      <div>

        <div className="boards">{boards}</div>

        <button>Toggle</button>

      </div>

    );

  }

});

​

ReactDOM.render(

  <BoardSwitcher numBoards={3} />,

  document.getElementById('container')

);